@erlend Yes, that's correct, thanks!
In the case of dbzer0, I choose to simplify it a little bit. The biggest community on dbzer0, !piracy@lemmy.dbzer0.com, has over 40k subscribers, while it's second biggest community (!adhd@lemmy.dbzer0.com) is only one tenth of the size at 4k subs. So defedding from only the biggest community has an outsized impact on the rest of the server as well.
But for sure, the granularity in defedding is interesting and worth a followup!